1. Field of the Invention
The present invention relates to a method of fabricating an oxide superconducting film, and more particularly, it relates to a method of fabricating an oxide superconducting film using laser ablation or laser deposition.
2. Description of the Background Art
With recent development of laser units, there has been proposed a laser deposition technique of applying a laser beam to a target for vaporizing or sputtering the target material and forming a film on a substrate (refer to "Saisentan Laser Kako Gijutsu" edited by Hiromichi Kawasumi, CMC Shuppan, for example).
Such a laser deposition technique has the following features:
(1) The film is generally formed at a high speed.
(2) The composition can be easily controlled.
In particular, laser ablation with an excimer pulse laser beam, which has high energy density of at least 0.5 to 1 J/cm.sup.2, is highlighted as means for forming an oxide superconducting thin film of Y-Ba-Cu-0, Bi-Sr-Ca-Cu-0 or the like, due to its capability of temperature reduction through photochemical reaction (refer to Appl. Phys. Lett. 53, 517 (1988) by C. C. Chang et al., for example).
It has been proved that the speed of film formation by laser ablation is proportionate to the frequency of a laser beam as used. If the frequency of a laser beam for forming an oxide superconducting film of Y-Ba-Cu-O, Bi-Sr-Ca-Cu-0 or the like is simply increased, however, it is difficult to incorporate oxygen, which must be contained in such an oxide superconducting film, since the speed of film formation is too high. When an oxide superconductor contains insufficient oxygen, its critical temperature T.sub.C is reduced. Thus, it is inexpedient to increase the frequency of the laser beam in order to simply improve the speed of film formation.
In more concrete terms, it is possible to form a Y-Ba-Cu-0 film of about 1 to 2 .ANG. in thickness every pulse by laser ablation with an ArF gas laser, for example. Thus, a film of 18000 .ANG. to 36000 .ANG. in thickness can be formed per hour with a laser beam of 5 Hz, for example. However, if a film is formed with a laser beam of 10 Hz, for example, sufficient oxygen cannot be incorporated into the as-formed oxide superconducting film since the speed of film formation is too high, although the amount of film formation is theoretically doubled per unit time.